It appears as though the briachilis muscle is attached a small distance from the elbow joint and I assume they are suggesting that the briachilis muscle is the primary and dominating support for the forearm. If I understand the question correctly the attachment of the briachlis muscle to the forearm is the pivot point. Therefore the force and torque on the elbow joint E exactly counterbalances the sum of the torque (force * distance * cosine angle between them) on the other side. Therefore the force on joint E will be roughly upward (opposite gravity) if my interpretation of the question is correct. Make sense?